Tandem pump

ABSTRACT

An apparatus comprising a tandem pump which includes first and second pump sections driven by a rotation shaft, and a housing defining a pump receiving portion including a first pump chamber receiving the first pump section and a second pump chamber receiving the second pump section. The first and second pump chambers are separated by a partition. The partition is positioned by the housing at least in the axial direction of the rotation shaft.

BACKGROUND OF THE INVENTION

The present invention relates to a tandem pump capable of increasing a first fluid pressure in a first hydraulic circuit and a second fluid pressure in a second hydraulic circuit by using one driving source (such as a motor).

A published Japanese patent Application Publication No. 2007-177687 shows a tandem pump including first and second driving gears of first and second pumps, a drive gear driving the driving gears and a center plate separating the first and second driving gears axially.

SUMMARY OF THE INVENTION

In the tandem pump of the above-mentioned patent document, the center plate is not positioned in the axial direction. Accordingly, a pressure difference, if produced between the first and second pumps, tends to shift the center plate from the higher pressure side toward the lower pressure side. This shift of the center plate causes interference between the center plate and the driving gear on the lower pressure side and thereby increases the friction therebetween. On the higher pressure side, the center plate moves away from the driving gear, and increases the leakage.

Therefore, it is an object of the present invention to provide a tandem pump adapted to restrain the friction and the leak.

According to one aspect of the invention, an apparatus includes at least a tandem pump. The tandem pump comprises: a rotation shaft extending in an axial direction; first and second pump sections (or gear sections) driven by the rotation shaft; a housing defining a pump receiving portion including a first pump chamber receiving the first pump section and a second pump chamber receiving the second pump section; and a partition separating the first and second pump chambers from each other. The partition is so arranged that the position of the partition is determined, at least in the axial direction, by the housing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a hydraulic circuit diagram showing a hydraulic system including a tandem pump P according to a first embodiment of the present invention.

FIG. 2 is a front view showing a z positive side of the tandem pump P.

FIG. 3 is a sectional view taken across a line I-I shown in FIG. 4.

FIG. 4 is a z axis direction sectional view of FIG. 2 showing a longitudinal or axial section of the tandem pump P.

FIG. 5 is a perspective view of a center plate (400) shown in FIG. 4.

FIG. 6 is a perspective view of a (first) side plate (150) shown in FIG. 4.

FIG. 7 is a perspective view of a leaf spring (300) shown in FIG. 2.

FIG. 8 is a z axis direction sectional view of a tandem pump P according to a second embodiment of the present invention.

FIG. 9 is a z axis direction sectional view of a tandem pump P according to a third embodiment.

FIG. 10 is a perspective view showing a first center plate (400P) shown in FIG. 9.

FIG. 11 is a perspective view showing a second center plate (400S) shown in FIG. 9.

FIG. 12 is a z axis direction sectional view of a tandem pump P according to a fourth embodiment.

FIG. 13 is a z axis direction sectional view of a tandem pump P according to a fifth embodiment.

DETAILED DESCRIPTION OF THE INVENTION Embodiment 1 [Hydraulic Circuit]

A tandem pump P is applied to a hydraulic unit H/U as shown in a circuit diagram of FIG. 1, according to a first embodiment of the present invention (and subsequent embodiments). Hydraulic unit H/U is connected between a master cylinder M/C and wheel cylinders W/C. Tandem pump P is a combination of a first pump P1 and a second pump P2, which are driven by a single common drive shaft (110), and so arranged that first and second pumps P1 and P2 are equal in the discharge quantity per unit time and the discharge pressure.

First pump P1 is connected with a P subsystem, and second pump P2 is connected with an S subsystem. First and second pumps P1 and P2 are arranged to supply the respective discharge pressures to the P and S subsystems independently. Tandem pump P and other components (such as valves GV-IN, GV-OUT, IN-V, and OUT-V) in the hydraulic circuit are controlled by a control unit CU.

This hydraulic brake system includes two independent brake subsystems, the P subsystem including a P route hydraulic circuit 10P and the S subsystem including an S route hydraulic circuit 20S. In this example, these two circuits 10P and 20S are arranged in a so-called X piping arrangement. The P route circuit 10P is connected to wheel cylinder W/C(FL) for a front left wheel of the vehicle, and wheel cylinder W/C(RR) for a rear right wheel. The S route circuit 20S is connected to wheel cylinder W/C(FR) for a front right wheel, and wheel cylinder W/C(RL) for a rear left wheel. It is optional to employ, for the brake circuit, arrangements other than the X piping arrangement. In this example, a wheel cylinder set including the four wheel cylinders is divided into a first subset including two of the fourth wheel cylinders and a second subset including the other two of the fourth wheel cylinders.

A brake pedal BP is arranged to transmit a driver's brake pedal operation through a brake booster BS and an input rod IR, to a master cylinder M/C. This master cylinder M/C is a tandem master cylinder including two pistons arranged in tandem to define two fluid pressure chambers in the cylinder. These two pressure chambers are arranged to receive the supply of a brake fluid from a reservoir tank RES. The first pressure chamber is connected with the first brake circuit 10P, and the second pressure chamber is connected with the second brake circuit 20S.

When brake pedal BP is depressed, the master cylinder M/C produces fluid pressures (master cylinder pressures Pmc) in the two pressure chambers in accordance with the brake pedal depression quantity, and supplies the produced master cylinder pressures Pmc, respectively, to first and second brake circuits 10P and 20S. A cup-shaped seal member (of known type) is provided on the outer circumference of each master cylinder piston, and arranged to shut off the connection between reservoir tank RES and the corresponding pressure chamber to enable a pressure increase in the corresponding pressure chamber at the time of piston stroke. In this case, the brake fluid is not supplied from reservoir tank RES to brake circuits 10P and 20S. The brake fluid is supplied only from the pressure chambers of master cylinder M/C to brake circuits 10P and 20S.

When brake pedal BP is returned, the master cylinder pistons are returned by respective return springs (provided in the pressure chambers). In this case, the cup-shaped seal members make the fluid connection between reservoir tank RES with the pressure chambers again, and thereby enable the supply of the brake fluid from reservoir tank RES to the pressure chambers, again. The following explanation is directed mainly to first brake circuit 10P.

Brake circuit 10P includes a gate-out valve GV-OUT(P) connected between an upstream second passage 10 n leading to master cylinder M/C, and a downstream second passage 10 k extending toward wheel cylinders W/C. Gate-out valve GV-OUT(P) is a normally-open proportional solenoid valve. A check valve 10 p is disposed in a passage 10 j connected in parallel to gate-out valve GV-OUT(P), and arranged to prevent the fluid flow in the direction from the downstream side (near the wheel cylinders W/C) to the upstream side (toward master cylinder M/C).

Downstream passage 10 k bifurcates into a first branch circuit 10 a extending to a first outlet point connected with one of the wheel cylinders W/C(FL, RR) and a second branch circuit 10 b extending to a second outlet point connected to the other of the wheel cylinders W/C(FL, RR) of the P subsystem. First and second flow-in valves IN/V(FL, RR) are provided, respectively, in the first and second branch circuits 10 a and 10 b. The flow-in valves IN/V are normally-open proportional solenoid valves.

A check valve 10 q is disposed in a passage 10 l connected in parallel to the first flow-in valve IN/V(FL), and arranged to prevent the fluid flow from the upstream side to the downstream side. Similarly, a check valve 10 r is disposed in a passage 10 m connected in parallel to the in the second flow-in valve IN/V(RR), and arranged to prevent the fluid flow from the upstream side to the downstream side.

A first flow-out valve OUT/V(FL) is disposed in a first return passage 10 c extending from the first outlet point (connected with wheel cylinder W/C(FL)) to a confluent return passage 10 e. A second flow-out valve OUT/V(RR) is disposed in a second return passage 10 d extending from the second outlet point (connected with wheel cylinder W/C(RR)) to the confluent return passage 10 e. First and second flow-out valves OUT/V are normally-closed on-off solenoid valves. The confluent return passage 10 e extends to a reservoir 16 provided in hydraulic unit H/U.

A gate-in valve GV-IN(P) is provided in a first passage log which is connected with the upstream second passage 10 n on the upstream side of gate-out valve GV-OUT(P). Gate-in valve GV-IN(P) is a normally-closed on-off solenoid valve arranged to open or close the first passage 10 g. First passage 10 g joins with a return passage 10 f extending from reservoir 16, and forms a suction (or inlet) passage 10 h.

The pump P is provided as a secondary pressure source in addition to master cylinder M/C. Pump P of this example is a tandem type gear pump including the first pump P1 (for the P side) and second pump P2 (for the S side) both driven by an electric motor M. The suction (inlet) side of first pump P1 is connected with the suction circuit 10 h. The discharge (outlet) side of first pump P1 is connected with a discharge (outlet) circuit 10 i, and further connected, through the discharge circuit 10 i, with the downstream side second circuit 10 k.

A check valve 10 s is provided in return circuit 10 f, and arranged to prevent the fluid flow from first circuit 10 g (gate-in valve GV-IN(P)) to reservoir 16. A check valve 10 u is provided in discharge circuit 10 i and arranged to prevent the fluid flow from downstream second passage 10 k (gate-out valve GV-OUT(P)) or from branch circuits 10 a and 10 b (wheel cylinders W/C), to first pump P1 (discharge side). The brake circuit 20S is constructed in the same manner as the brake circuit 10P, as shown in FIG. 1 (in which the brake circuits 10P and 20S are arranged in a manner of bilateral symmetry).

[Brake Control]

In a normal brake operation, hydraulic unit H/U enables a boosting control (or pressure increasing control)(as mentioned below), an automatic brake control such as ACC (adaptive cruise control: control for controlling a distance between vehicles) and VDC (vehicle dynamics control or vehicle behavior control), and anti-skid brake control. In the automatic brake control such as the vehicle behavior control, the control unit CU closes the gate-out valve GV-OUT(P), and opens the gate-in valve GV-IN(P)(in the case of the brake circuit 10P, as an example). At the same time, by driving the pump P, the hydraulic unit HU supplies the brake fluid from master cylinder M/C, through passages 10 g and 10 h and discharge circuit 10 i, toward the branch circuits 10 a and 10 b.

Furthermore, the control unit CU controls the gate-out valve GV-OUT(P) or the flow-in valves IN/V(FL, RR) to produce a desired wheel cylinder fluid pressure Pwc* corresponding to a braking force required for stabilizing the vehicle behavior. The brake circuit 20S is controlled in the same manner.

At the time of anti-skid brake control, the control unit CU opens the flow-out valve OUT/V(FL), and closes the flow-in valve IN/V(FL) in the case of wheel FL, as an example. By so doing, the control unit CU decreases the wheel cylinder pressure by discharging the brake fluid from wheel cylinder W/C(FL) to reservoir 16. When wheel FL recovers from a locking tendency, the control unit CU holds the wheel cylinder pressure by closing the flow-out valve OUT/V(FL). Moreover, control unit CU increases the wheel cylinder pressure appropriately by driving the pump P and opening the flow-in valve IN/V(FL). Pump P functions to return the brake fluid drained to reservoir 16 at the time of pressure decreasing operation, to the second passage 10 k.

Thus, as shown in FIG. 1, the hydraulic brake system includes at least: a wheel cylinder set including a first subset including at least a first wheel cylinder (W/C) provided for braking a first wheel of a vehicle and a second subset including at least a second wheel cylinder (W/C) provided for braking a second wheel of the vehicle; and a hydraulic (valve) system including a first subsystem including at least a first control valve (IN-V, OUT-V) and connecting the first pump section with the first wheel cylinder to increase the fluid pressure of the first wheel cylinder, and a second subsystem including at least a second control valve (IN-V, OUT-V) and connecting the second pump section with the second wheel cylinder (W/C) to increase the fluid pressure of the second wheel cylinder.

[Tandem Pump]

FIG. 2 shows a z positive side of the tandem pump P. FIG. 3 shows tandem pump P in a section taken across a line I-I shown in FIG. 4. FIG. 4 is a z axis (axial) sectional view of tandem pump P. In FIG. 3, a leaf spring 300 is omitted. FIG. 5 shows a center plate (partition) 400 in perspective. FIG. 6 shows a first side plate 150 in perspective. FIG. 7 shows the leaf spring 300 in perspective. First and second side plates 150 and 160 are substantially identical in shape, so that only the first side plate 150 is shown in FIG. 6.

In the following explanation, an x positive direction in which an x axis extends is a direction from a driven shaft 120 to a driving shaft 110 in a pump assembly 100, a y positive direction in which a y axis extends is a direction which is perpendicular to the x positive direction and which extends toward the position of seal blocks 200, and a z positive direction of a z axis is an axial direction which is parallel to the axis (Op) of driving shaft 110, and which extends toward a first end of driving shaft 110 adapted to be connected with motor M.

Tandem pump P is a pump of a type driving first and second pumps P1 and P2 simultaneously with the single common driving shaft 110. First and second pumps P1 and P2 are substantially identical in construction. First and second pumps P1 and P2 produce discharge pressures for the P and S circuits, respectively or independently. Center plate 400 (serving as a partition) is interposed (axially) between first and second pumps P1 and P2, and arranged to seal first and second pumps P1 and P2 from each other.

[Housing]

Housing 1 of tandem pump P is composed of a main housing member 10 (first housing member) and a cover member 20 (second housing member), which are made of metallic material which is aluminum alloy in this example. Main housing member 10 includes an end wall (first end wall) formed with a driving shaft support hole 11 and a surrounding (or circumferential) wall defining a pump receiving portion 12 which, in this example is an inside cavity in the form of a stepped cylinder. Pump assembly 100 is inserted into pump receiving portion 12 from a z negative side (from the left side as viewed in FIG. 4). Driving shaft 110 is supported rotatably through bushing by the drive shaft support hole 11.

The surrounding wall of main housing member 10 includes a step 13 formed in pump receiving portion 12. Pump receiving portion 12 is composed of a first (smaller cylindrical) portion 14 (serving as a first side receiving portion) and a second (larger cylindrical) portion 15 which is greater in cross sectional size or in diameter than first portion 14 (and which can serve as a middle receiving portion located axially between the first side receiving portion 14 and a second side receiving portion on the z negative side). Step 13 is formed between first and second portions 14 and 15. Step 13 includes an annular shoulder surface facing in the z negative direction (second axial direction) to abut against the center plate 400 of pump assembly 100 and thereby to limit the movement of pump assembly 100 in the z positive direction (first axial direction). The surrounding wall of main housing member 10 includes a first wall portion surrounding and defining the first (smaller) portion 14, and a second wall portion surrounding and defining the second (larger) portion 15 located on the z negative side of the first (smaller) portion 14.

As shown in FIGS. 2 and 3, the cylindrical pump receiving portion 12 is defined by an inside circumferential (or cylindrical) surface including a first region 12 a used as a positioning abutment surface and a second region 12 b. The first region 12 a is adapted to abut on the seal block 200 shown in FIGS. 2 and 3, and thereby to position the pump assembly 100. Therefore, first region 12 a is formed more accurately than the second region 12 b. Main housing member 10 is formed with discharge circuits 10 h and 20 h connecting the pump receiving portion 12 fluidly with the outside. Discharge circuits 10 i and 20 i are located on the x positive side.

Cover member 20 is fixed to main housing member 10 by bolts B. Cover member 20 is located on the z negative side of main housing member 10. Pump assembly 100 is enclosed liquid-tightly in the pump receiving portion 12 by cover member 20 and main housing member 10. Cover member 20 is a cup-shaped member having a bottom. Cover member 20 includes a base portion (forming a second end wall axially confronting the first end wall formed with the drive shaft support hole 11) and a (cylindrical) projecting portion 21 projecting in the z positive direction from the base portion and receiving second pump P2. The (cylindrical) projecting portion 21 is provided with a seal ring 33 fit in an annular groove formed in the outside circumferential surface of projecting portion 21, and inserted liquid-tightly in the pump receiving portion 12 of main housing member 10. The projecting portion 21 of cover member 20 includes a surrounding wall defining a second side receiving portion which is similar to the first portion 14 (defining the first side receiving portion) and which receives the second pump P2 and second side plate 160 like the first portion 14 of pump receiving portion 12.

[Details of Pump Assembly]

Pump assembly 100 includes first and second seal blocks 200, drive shaft 110, driven shaft 120, first and second driving gears 130 and first and second driven gears 140, first and second side plates 150 and 160 (a pair of side plates) and center plate 400.

Pump assembly 100 is temporarily united by C-shaped leaf springs 300. Seal blocks 400 are shorter in the width in the x direction than the first and second side plates 150 and 160. Center plate 400 liquid-tightly defines first and second discharge regions (pump chambers) Dout1 and Dout2 formed, respectively, on the radial outer side of first and second side plates 150 and 160.

First driving gear 130P and first driven gear 140P for the P route circuit are provided on the z positive side of center plate 400. Second driving gear 130S and second driven gear 140S for the S route circuit are provided on the z negative side of center plate 400. As shown in FIG. 4, the first driving and driven gears 130P and 140P are located axially (along the z axis) between the center plate 400 on the z negative side and the first side plate 150 on the z positive side. The second driving and driven gears 130S and 140S are located axially between the center plate 400 on the z positive side and the second side plate 160 on the z negative side. Center plate 400 is located axially between the first driving and driven gears 130P and 140P on the z positive side, and the second driving and driven gears 130S and 140S on the z negative side.

A P route discharge circuit 10 i is formed in the region which is located on the z positive side of center plate 400 and on the x positive side of first side plate 150. An S route discharge circuit 20 h is formed in the region which is located on the z negative side of center plate 400 and on the x positive side of second side plate 160. S route discharge circuit 20 i is formed by drilling center plate 400.

Two of the seal blocks 200 are disposed, respectively, on the y positive side of first and second side plates 150 and 160. As shown in FIG. 4, along the z axis, the center plate 400 is located between the first pump P1 for the P route on the z positive side (the right side as viewed in FIG. 4) and the second pump P2 for the S route on the z negative side (the left side in FIG. 4). However, it is optional to reverse the positions of the first and second pumps of the P route and S route so that first pump P1 for the P route is located on the z negative side and second pump P2 for the S route is located on the z positive side.

The center plate 400, first and second side plates 150 and 160 and first and second seal blocks 200 are bilaterally symmetrical with respect to an imaginary straight line II-II (representing an imaginary flat median plane) in a radial plane or cross sectional plane (x-y plane) as shown in FIG. 2. This II-II line is located at the middle between driving shaft 110 and driven shaft 120. Moreover, the leaf spring 300 shown in FIG. 2 is bilaterally symmetrical with respect to the II-II line, and leaf spring 300 is arranged to produce resilient forces symmetrical with respect to the II-II line. The II-II line extends along the y axis between the driving and driven shafts 110 and 120 both extending along the z axis.

In the x-y plane, as shown in FIG. 2, pump assembly 100 and leaf spring 300 are set in point contact with each other at three contact points A, B and C. The first contact point A is located on the y positive side of the seal block 200 shown in FIG. 2. The second and third contact points B and C are located at two x end portions 152 (162 in the case of second side plate 160) in a y negative side 151 (161) of the side plates 150 (160), respectively, as shown in FIG. 2.

First contact point A is located on the II-II line (the median plane) which extends through the middle point M between the axes Op and Os of driving shaft 110 and driven shaft 120, in parallel to the y axis. Second and third contact points B and C are located on the y negative side of an imaginary III-III straight line passing through the axes Op and Os (and representing an imaginary transverse plane), one on the x positive side of the II-II line and the other on the x negative side.

The point contact in the x-y plane means a line contact in the x-y-z space on a straight line extending along the z axis. Leaf spring 300 shown in FIG. 2 contacts with the seal block 200 along a straight line passing through contact point A and extending along the z axis, and further contacts with the (first) side plate 150 (160) along straight lines passing through contact points B and C, respectively, and extending along the z axis.

Accordingly, pump assembly 100 is held at the first contact point A from the y positive side, and urged toward the y positive side at the second and third points B and C by leaf spring 300. With this three-point support structure at the points A, B and C, the leaf spring 300 can press the seal block 200 from the y-axis positive side against the first side plate 150 (160), and thereby unite or bind the pump assembly 100 provisionally. The second side plate 160 and second seal block 200 are bound and united in the same manner as shown in FIG. 2.

Seal blocks 200 are narrower in the width measured along the x axis than first and second side plates 150 and 160. Therefore, each of seal blocks 200 is urged stably toward the y negative side with leaf spring 300 including a one-point support portion supporting the y positive side of seal block 200 at point A, and a two-point support portion supporting the y negative side of the first or second side plate 150 or 160 at points B and C.

[Drive Shaft and Driven Shaft]

Drive shaft 110 is connected with first and second driving gears 130P and 130S made of a ferrous material so that they rotates as a unit. Driven shaft 120 is connected with first and second driven gears 140P and 140S made of the ferrous material so that they rotates as a unit. As shown in FIG. 4, driving shaft 110 extends, along the z axis, from a second (left) end to a first (right) end (z positive end) which is adapted to be connected with the motor not shown in FIG. 4. The gears 130P, 130S, 140P and 140S are spur gears. On each of the first and second sides for the P and S circuits, driving gear 130 (130P, 130S) and driven gear 140 (140P, 140S) are engaged with each other in the form of a spur gear set as shown in FIG. 3, so that driven shaft 120 is driven by driving shaft 110.

[Center Plate]

Center plate 400 is a circular disc-shaped member including a step as best shown in FIG. 5. Center plate 400 is an integral member formed by a forming process of uniting a plate (third side plate) 150′ (FIG. 4) adapted to be in sliding contact with driving and driven gears 130P and 140P, and another plate 160′ (FIG. 4) adapted to be in sliding contact with driving and driven gears 130S and 140S.

Center plate 400 includes a step 410, a smaller section 420 having a smaller diameter and lying on the z positive side of step 410, and a larger section 430 having a larger diameter larger than the diameter of smaller section 420, and lying on the z negative side of step 410. Center plate 400 further includes a drive shaft hole 401 receiving drive shaft 110 rotatably, and a driven shaft hole 402 receiving driven shaft 120 rotatably.

Seal members 34 and 35 are received, respectively, in annular grooves 401a and 402 a formed in drive shaft 110 and driven shaft 120 (as shown in FIG. 4). Seal members 34 and 35 seal the clearances around the drive shaft 110 and driven shaft 120, respectively, and thereby seal off the first and second pumps P1 and P2 from each other.

The smaller section 420 of center plate 400 includes a z positive side 421 including a sliding surface 421 a adapted to be in sliding contact with the driving and driven gears 130P and 140P (as shown in FIG. 4 and FIG. 5), and an abutting surface 421 b formed on the y positive side of the sliding surface 421 a (as shown in FIG. 5) and adapted to be abut on the first seal block 200 liquid-tightly.

Similarly, the larger section 430 of center plate 400 includes a z negative side 431 including a sliding surface 431 a adapted to be in sliding contact with the drive and driven gears 130S and 140S (as shown in FIG. 4), and an abutting surface 431 b formed on the y positive side of the sliding surface 431 a and adapted to be abut on the second seal block 200 liquid-tightly.

The sliding surfaces 421 a and 431 a are formed around the drive shaft hole 401 and driven shaft hole 402 in inner regions of z positive and negative sides 421 and 431 of center plate 400, respectively. FIG. 5 shows only the z positive side 421 of the smaller section 420, and explanation on the sliding surface 431 a and abutting surface 431 b of the larger section 430 is omitted since the sliding surfaces 421 a and 431 a, and the abutting surfaces 421 b and 431 b are substantially identical in shape and position.

Sliding surface 421 a is an 8-shaped region including a first annular portion surrounding the drive shaft hole 401, and a second annular portion surrounding the driven shaft hole 402. Gears 130P and 140P can slide liquid-tightly on the sliding surface 421 a. Between the gear sliding surface 421 a and the seal block abutting surface 421 b, there are formed sliding surfaces 158 and seal block sliding surfaces 210 and 220, as shown in FIG. 5.

Seal block abutting surface 421 b is a C-shaped region surrounding a suction passage Din. Suction passage Din is defined liquid-tightly by the C-shaped abutting surface 421 b and an inlet side recessed portion 421 c which is formed in the 8-shaped sliding surface 421 a on the y positive side toward the abutting surface 421 b, at the middle of the 8-shaped sliding surface 421 a in the x direction.

An outlet side recessed portion 421 d is formed on the opposite side (y negative side) of the sliding surface 421 a. The 8-shaped sliding surface 421 a includes a connecting portion which is formed, along the x axis, between the first annular portion surrounding the drive shaft hole 401 and the second annular portion surrounding the driven shaft hole 402, and which is located between the inlet side recessed portion 421 c and outlet side recessed portion 421 d, along the y axis. Outlet side recessed portion 421 d is located on the outlet or discharge side of the driving and driven gears 130P and 140P, and arranged to cause the outlet pressure to flow smoothly to the discharge region Dout1 formed on the outer side of the sliding surface 421 a.

A (smaller) seal ring 31 is fit in an annular groove 422 a formed in the (cylindrical) circumference 422 of smaller section 420. Similarly, a (larger) seal ring 32 is fit in an annular groove 432 a formed in the (cylindrical) circumference 432 of larger section 430. There are further provided, respectively, in drive and driven shafts 110 and 120, seal rings 34 and 35 for sealing off the first and second pumps P1 and P2 from each other.

The circumference 432 of larger section 430 is formed with at least one opening of inlet circuit 20 h for supplying an inlet pressure to second pump P2 for the S circuit. The supply of the inlet pressure to first pump P1 for the P circuit is achieved by inlet circuit 10 h formed in main housing member 10 on the z positive side of first plate 150 (as shown in FIG. 3).

The (external) annular step 410 of center plate 400 includes an annular step surface which faces in the z positive direction (first axial direction) and which abuts on the annular shoulder surface of the (internal) step 13 of main housing member 10 so that the axial movement of center plate 400 in the z positive direction is limited by the shoulder surface of step 13. Cover member 20 includes cylindrical projecting portion 21 projecting in the z positive direction and terminating at an annular forward end 22, which abuts on an outer circumference portion 433 of the second side (z negative side) 431 of the larger section 430. Therefore, center plate 400 is clamped axially between the shoulder surface of step 13 of main housing member 10 and the forward end 22 of cover member 20 so that center plate 400 is unable to move in the axial direction along the z axis.

[Side Plates]

First and second side plates 150 and 160 are members having the same 8-shaped form as shown in FIG. 6. Each of side plates 150 and 160 is formed with a drive shaft hole 153 or 163 and a driven shaft hole 154 or 164. FIG. 6 shows only the first side plate 150 and the following explanation is directed mainly to first side plate 150 since first and second side plates 150 and 160 are substantially identical and arranged substantially symmetrical with respect to an imaginary center radial plane (x-y plane) at the middle axially between the first and second side plates 150 and 160.

Discharge region Dout1 (or Dout2) is formed around side plate 150 (or 160), as shown in FIG. 2 and FIG. 4. Side plate 150 (160) includes a first annular section surrounding drive shaft hole 153 (163) and a second annular section surrounding driven shaft hole 154 (164). Side plate 150 (160) further includes a middle recessed portion 150 b (160 b) recessed in the y negative direction, from a y positive side 150 a (160 a), between the first annular section on the x positive side and the second annular section on the x negative side.

The middle recessed portion 150 b (160 b) of side plate 150 (160) is connected with the inlet or suction circuit 10 i (20 i) and arranged to supply the operating fluid therethrough. The y positive side 150 a (160 a) of side plate 150 (160) includes a driving side sealing curved surface 158 a (168 a) on the x positive side of the middle recessed portion 150 b (160), and a driven side sealing curved surface 158 b (168 b) on the x negative side of the middle recessed portion 150 b (160 b). The sealing curved surfaces are used for sealing with the corresponding seal block 200.

First side plate 150 includes a (8-shaped) z negative side surface 159 adapted to be in sliding contact with the first driving and driven gears 130P and 140P liquid-tightly. Similarly, second side plate 160 includes a (8-shaped) z positive side surface 169 adapted to be in sliding contact with the second driving and driven gears 130S and 140S liquid-tightly.

First side plate 150 includes a z positive side surface 155 in which a first seal ring 170 is provided , as shown in FIG. 4. Second side plate 160 includes a z negative side surface 165 in which a second seal ring 180 is provided. Each of first and second seal rings 170 and 180 surrounds the drive shaft 110 and driven shaft 120 (as shown in FIG. 2). First seal ring 170 abuts on main housing member 10. Second seal ring 180 abuts on cover member 20.

Thus, each of the seal rings 170 and 180 surrounds the sliding surfaces between the drive and driven shafts 110 and 120 and the first or second side plate 150 or 160, and thereby defines the suction region Din (first fluid chamber) sealed off liquid-tightly from the discharge region Dout (second fluid chamber) formed on the outer side of the seal ring 170 or 180.

The side plate 150 (160) includes two grooves 156 (166) recessed radially inwards (along the x axis toward the center M, as shown in FIG. 2), respectively, from the x-axis positive and negative end surfaces 157 (167), at the middle of the width in the z-axis direction (as shown in FIG. 6) (by cutting, for example).

Therefore, in the x-y plane, on each of the x-axis positive side and negative side of side plate 150 (160), the bottom of the groove 156 (166) and the x-axis end surface 157 (167) are curved, so as to form a rounded end like a circular arc, with unequal curvatures. The z-axis width of each of the grooves 156 (166) as measured along the z axis, is greater than the z-axis width of each of metal bands 301 and 302 of the leaf spring 300.

Thus, the grooves 156 and the z positive side surface 151 of first side plate 150 are formed so as to have different curvature, and the grooves 166 and the z negative side surface 161 of second side plate 160 are formed so as to have different curvature. Moreover, the grooves 156 and 166 have the z-axis width greater than the z-axis width of the metal bands 301 and 302. Thus, the grooves 156 (166) of side plate 150 (160) are formed so as to prevent abutment between the leaf spring 300 and the grooves 156 (166) when leaf spring 300 is fit over pump assembly 100.

Therefore, the leaf spring 300 touches the side plates 150 (160) only at the contact points B and C with the inner sides of both end portions 321 and 322, and thereby forms the three-point support structure together with the contact point A of abutment between leaf spring 300 and seal block 200. The grooves 156 (166) prevent interference of legs 320 of leaf spring 300 with the x-axis ends 157 (167) of side plates 150 (160), and ensure the three-point support structure.

[Seal Blocks]

The following explanation is directed mainly to the first seal block 200 shown in FIG. 2 and the first side plate 150. The second seal block 200 and second side plate 160 are substantially identical to the first seal block 200 and first side plate 160, and arranged substantially symmetrical with respect to the imaginary center radial plane (x-y plane) at the middle axially between the first and second side plates 150 and 160. The seal block 200 shown in FIG. 2 is placed between the abutting surface 12 a of housing 1 on the y positive side and the side plate 150 (160) on the y negative side, and designed to achieve sealing. Seal block 200 includes an arched y positive side surface 240 facing in the y positive direction in the form of a convex surface curved like a circular arc and abutting on the abutting surface 12 a of housing main member 10 for positioning, and a y negative side surface abutting on the side plate 150 (160). The y negative side surface of seal block 200 includes a driving side arched (concave) sealing surface 210 (shown in FIGS. 2 and 3) and a driven side arched (concave) sealing surface 220 (shown in FIGS. 2 and 3) which are curved like a circular arc for abutting liquid-tightly, respectively, on the driving side arched (convex) sealing surface 158 a (shown in FIG. 6)(168 a and the driven side arched (convex) sealing surface 158 b (shown in FIG. 6)(168 b) of the 8-shaped side plate 150 (160). The mating (concave and convex) arched surfaces of the seal block 200 and the side plate 150 (160) are cylindrical surfaces having the same curvature.

In the pump driving state, the tops (131) of teeth of the driving gear 130 rotate on the radial outer side of the corresponding sealing surface 158 a (168 a) of the side plate 150 (160), and the tops (141) of teeth of the driven gear 140 rotate on the radial outer side of the corresponding sealing surface 158 b (168 b) of side plate 150 (160).

Therefore, these sealing surfaces of seal blocks 200 are ground by the tops of the gear teeth so as to form tooth contact surfaces (211, 221). The thus-formed structure can ensure the sealing by reducing the clearance almost to zero while avoiding contact between the sealing surfaces and the gear teeth.

Seal block 200 further includes a middle recessed portion 230 which extends, between the sealing surfaces 210 and 220 (as shown in FIG. 2), over the entire axial width along the z axis, and which is recessed in the y positive direction. Together with the middle recessed portion 150 b (160 b) of the side plate 150 (160), this middle recessed portion 230 of seal block 200 defines an inlet region Din for introducing the operating fluid (oil) from the suction circuit 10 i (20 i) to the engaging portions of the driving and driven gears 130 and 140.

The y positive side surface 240 of seal block 200 is curved like a circular arc, as shown in FIG. 2. Seal block 200 includes z positive and negative sides 201 (FIG. 2) and 202 formed with (third and fourth) step portions 251 (FIG. 2) and 252, respectively. Each of the step portions 251 and 252 has a convex shape bulging in the y positive direction up to a y positive side end (peak) 253 or 254 which is located on the median plane represented by the II-II straight line, and which abuts on the leaf spring 300 and thereby defines the first contact point A.

Seal block 200 further includes a projecting portion 250 projecting in the y positive direction between the step portions 251 and 252. The metal bands 301 and 302 of leaf spring 300 abut against the seal block 200 at the contact point A. Thus, leaf spring 300 is fit over the projecting portion 250 of seal block 20 and thereby positioned. Moreover, leaf spring 300 abuts against the steps portions 251 and 252 of seal block 200, and thereby limits the movement of seal block 200 in the y positive direction.

The distance between the z positive side surface 155 of first side plate 150 and the z negative side surface 165 of second side plate 160 is set equal to the distance between the seal blocks 200 along the z axis. Therefore, the seal rings 170 and 180 provided in the first and second side plates 150 and 160 abut axially on the seal blocks 200 along the z axis, respectively. Thus, the driving side and driven side sealing surfaces 158 a (168 a) and 158 b (168 b) of the side plate 150 (160) and the sealing surfaces of the seal block 200 are sealed by the seal ring 170 (180) on the z positive or negative side end surface.

[Liquid Pressure Difference]

By the operation of the driving and driven gears 130 and 140 in the pump drive state, the operating fluid is sucked from the z negative side of the inlet passage Din, and discharged to from the z positive side. Therefore, the pressure difference is produced in the y negative direction by the pump operation between the higher pressure discharge side formed on the outer side around the pump assembly 100 and the seal block 200 (excepting the abutting surface) and the lower pressure suction side of the abutting surface of the seal block 200. By this pressure difference, pump assembly 100 is urged in the y positive direction, and seal block 200 is urged in the y negative direction and pressed against pump assembly 100. Therefore, the pressure difference acts to improve the sealing performance in the abutting surfaces between pump assembly 100 and seal block 200.

[Leaf Spring]

Leaf spring 300 shown in FIG. 7 is a resilient member for provisionary uniting or binding the pump assembly 100. Leaf spring 300 is bilaterally symmetrical, in the shape and elastic force, with respect to a median plane passing through a middle point A′ located at the middle in the dimension in the x direction. By the use of leaf spring 300, it is possible to avoid influence of elastic force decrease due to time degradation unlike a coil spring.

Leaf spring 300 includes the first and second metal bands 301 and 302 extending side by side (in parallel to each other) so as to describe the letter C from a first end 321 to a second end 322, and connecting portions 303˜306 connecting the first and second metal bands 301 and 302 like rungs of a ladder. Connecting portions 305 and 306 extend in the z direction, respectively, at the first and second ends 321 and 322 of leaf spring 300. Connecting portions 303 and 304 extend in the z direction so that the seal blocks 200 are placed between the connecting portions 303 and 304 in the x direction.

An engagement hole 311 is formed by connecting portions 303 and 304 on the y positive side and the first and second metal bands 301 and 302. The projecting portion 250 of seal block 200 is fit in the engagement hole 311. Engagement hole 311 facilitates the positioning operation at the time of assemblage.

Leaf spring 300 is curved so as to bulge in the y positive direction like a mountain, and to have a vertex at the middle A′ in the x dimension. The vertex point (or points) A′ is located on the II-II straight line as shown in FIG. 2, and the leaf spring 300 is designed to deform in the symmetrical manner with respect to the median plane (II-II). A middle portion 310 of leaf spring 300 straddles the seal block 200 and abuts against the seal block 200 so that the point A′ of leaf spring 300 is in point contact with the point A of seal block 200. In the assembled state, the points A and A′ coincide with each other.

On the both sides of the middle portion 310 in the dimension in the x direction, leg portions 320 extend in the y negative direction, respectively, to the first and second ends 321 and 322, and fit over the side plate 150 (160). The first and second ends 321 and 322 of leaf spring 300 abut on the side plate 150 (16) so that contact points B′ and C′ on the inner sides of first and second ends 321 and 322 are in point contact with the contact points B and C of the (first and second) side plate 150 (160), respectively.

The shapes of first and second side plates 150 and 160 are not limited to the illustrated example. Side plates 150 and 160 and leaf springs 300 may be shaped in other forms to produce the urging forces having components in the y positive direction and to prevent interference between the legs 320 and the end surfaces 157 and 167.

[Reduction of Friction and Leak]

Driving and driven gears 130 and 140 are identical in construction, between first and second pump P1 and P2 for the P and S circuits, and both pumps are driven by one and the same drive shaft 110. Moreover, the pump chambers Dout1 and Dout2 of first and second pumps P1 and P2 are formed by the first and second side plates 150 and 160 having the same shape and the first and second seal blocks 200 having the same shape. Therefore, in the normal state, the discharge flow rates and the discharge pressures are equal between the first and second pumps P1 and P2, so that center plate 400 receives forces by the equal discharge pressures on both sides along the z axis, and the forces acting on center plate 400 are balanced.

However, when either of the P and S circuits fails or when the pressures of the P and S circuits are controlled at different levels, the pressure on one side of center plate 400 becomes higher than the pressure on the other side, and the balance is lost among the force acting in the z direction on center plate 400, so that center plate 400 is pushed in the z positive direction or the z negative direction.

When, for example, center plate 400 is moved in z positive direction, the center plate 400 pushes the gears 130P and 140P axially, and increases the friction. On the other hand, the center plate 400 increases the clearance between center plate 400 and the gears 130S and 140S on the z negative side by being moved in the z positive direction away from the gears 130S and 240S, and thereby increases the leakage. When center plate 400 is moved in the z negative direction, the same problem arises in the reverse manner.

According to the first embodiment, an outer encasing or housing wall structure (10, 20) encases first and second pump sections (P1, P2) each including at least one rotating element (130, 140), and includes a surrounding (or circumferential) wall (formed by housing main body 10) surrounding the first and second pump sections disposed in a central region, a first end wall (formed by housing main member 10) and a second end wall (formed by cover member 20). There is further provided a partition or partition wall (formed by center plate 400) separating the first and second pump sections liquid-tightly (together with a seal member such as seal members 31, 32, 34 and 35). The partition includes a first abutting surface (or step surface formed by step 410) facing in a first axial direction (z positive direction) toward the first end wall, and a second abutting surface (end surface 433) facing toward the second end wall (20) in a second axial direction (z negative direction) opposite to the first axial direction. The first abutting (step) surface (410) and the second abutting (end) surface (433) surround a central region in which rotating elements (130, 140) of the first and second pump sections are disposed, and the first and second abutting surfaces (410, 433) may be both annular. The surrounding wall (formed by housing main member 10) includes a shoulder surface (formed by step 13) which faces in the second axial direction (z negative direction) and which may be annular, and the second end wall (formed by cover member 20) includes a projecting end surface (22) which faces in the first axial direction (z positive direction) and which may be annular. In the assembled state, the (annular) shoulder surface (13) of the surrounding wall (10) abuts axially on the (annular) first abutting (step) surface (410) of the partition (400), and thereby limits the movement of the partition (400) in the first axial direction. On the other hand, the (annular) projecting end surface (22) of the second end wall (20) abuts axially on the (annular) second abutting surface (433) of the partition (400) and thereby limits the movement of the partition (400) in the second axial direction. This partition structure holds the position of partition (400) fixed at the predetermined position without regard to the pressure states of the first and second pumps (for the P and S systems), and thereby prevent undesired increase in the friction and leak.

The second end wall (20) is fastened to the surrounding wall (10) by fastening devices (such as bolts B) extending axially (along the z axis), so that the second end wall (20) pushes the partition (400) in the first axial direction (z positive direction). This axial pushing force is applied, through the first abutting surface (410) of the partition (400), to the shoulder surface (13) of the surrounding wall (10), and the partition (400) is pushed in the first axial (z positive) direction against the surrounding wall (10). Furthermore, this pushing force acts to produce a friction force between the first abutting surface (410) of the partition (400) and the shoulder surface (13) of the surrounding wall (10), and this frictional force acts to restrain rotational movement of the partition (400) with respect to the surrounding wall (10).

The surrounding wall (10) receives the pushing force through the first abutting surface (410) and the shoulder surface (13). Therefore, this abutment structure can prevent the pushing force from being applied from the second end wall (20), to the rotating elements (130P, 140P, 130S and 140S) of the first and second pump sections, and thereby eliminates the need for controlling the tightening torque of the fastening devices (B) severely.

Effects of First Embodiment

(1) A tandem pump apparatus including at least a tandem pump which includes a first pump section (P1) including a first rotating element (130P, 140P) for producing a first fluid pressure, a second pump section (P2) including a second rotating element (130S, 140S) for producing a second fluid pressure, a rotating shaft (110) driving the first and second rotating elements, a housing including a housing wall structure (10, 20). The housing wall structure includes a surrounding wall (10) surrounding and defining a pump receiving portion or inside cavity (12) which includes a first discharge region (Dout1) receiving the first rotating element (130P, 140P) and a second discharge region (Dout2) receiving the second rotating element (130S, 140S), and a partition (400) extending in the pump receiving portion (12) and separating the first and second discharge regions liquid-tightly from each other. The partition (400) is engaged with the surrounding wall (10) so that the position of the partition (400) is determined by the surrounding wall (10) at least in an axial direction along the axis of the rotating shaft (110). This tandem pump apparatus can fix the axial position of the partition (400), and reduce the friction and the leak of the operating fluid.

(2) The housing wall structure (10, 20) is arranged to prevent rotational movement of the partition (400) about the axis of rotating shaft 110. Therefore, the tandem pump apparatus can fix the partition (400) securely.

(3) The housing wall structure (10, 20) includes a first housing member (10) including the surrounding wall (and the first end wall) and a second housing member (20) including the second end wall. Therefore, this structure makes it easier to install a pump assembly (100) including the first and second pump sections in the housing wall structure.

(4) The partition of the first embodiment is in the form of a plate member (400) which is separate from the first housing member (10), and which is positioned by being interposed or clamped, at the outer circumferential (or annular) portion (433), between the first housing member (10) and the second housing member (20). Therefore, this tandem pump apparatus can position the plate member (400) at a position avoiding interference with the rotating elements (130, 140) of the pump sections.

(5) The pump receiving portion (12) includes a first (smaller) portion (14) and a second (larger) portion (15) which is greater in the cross sectional size than the first portion, and the surrounding wall (10) of the first housing member (10) includes a first wall portion surrounding and defining the first (smaller) portion (14), a second wall portion surrounding and defining the second (larger) portion, and a step (13) which is formed between the first and second wall portions and which includes the shoulder surface in the pump receiving portion (12). The plate member (400) of the partition is positioned by being clamped between the step (13) of the first housing member (10) and the second housing member (20). Therefore, tandem pump apparatus can determine the position of the partition (400) relative to the surrounding wall (10) reliably. In the illustrated example, the pump receiving portion (12) is substantially circular in the cross section, and the plate member (400) is clamped between the first and second housing members (10, 20), in an outer annular zone surrounding a center zone in which the first and second pump sections are disposed, so that the plate member (400) is positioned securely.

(6) Each of the first and second pump sections includes a driving gear (130) drivingly connected with the rotation shaft (110) and a driven gear (140) engaged with the driving gear, the first pump section (130P, 140P) is interposed (axially) between a first side plate (150) and a first side portion (150′) of the partition (400), the second pump section (130S, 140S) is interposed (axially) between a second side plate (160) and a second side portion (160′) of the partition (400), and the first and second side portions (150′, 160′) are integral parts of the partition.

(7) The apparatus comprises the tandem pump (1); a wheel cylinder set including a first subset including at least a first wheel cylinder (W/C) provided for a first wheel of a vehicle and a second subset including at least a second wheel cylinder (W/C) provided for a second wheel of the vehicle; a hydraulic system (HU) including a first subsystem which includes at least a first control valve (IN-V, OUT-V)( and which connects the first pump section (P1) with the first wheel cylinder to increase a first fluid pressure of the first wheel cylinder, and a second subsystem which includes at least a second control valve (IN-V, OUT-V) and which connects the second pump section (P2) with the second wheel cylinder to increase a second fluid pressure of the second wheel cylinder. The apparatus may further comprises a control unit (CU) to control the first fluid pressure to the first wheel cylinder and the second fluid pressure to the second wheel cylinder, respectively, by controlling the first and second pump sections and the first and second control valves. Therefore, the hydraulic brake apparatus can fix the position of the partition (400) reliably and prevent undesired increase of the friction and leak even if one of the first and second systems becomes abnormal or if the first and second systems require different target pressure levels.

(8) A tandem pump comprises volume change preventing means, provided in the pump receiving portion (12), for preventing volume change of the first and second pump chambers (Dout1, Dout2), by being positioned by the housing. This tandem pump can prevent the volume changes in the first and second pump chambers, and thereby reduce the friction and the leak of the operating fluid. The volume change preventing means may include a partition (400) separating the first and second pump chambers. Alternatively, the volume change preventing means may include a means for preventing the partition (400) from being moved (at least in the axial direction)(by fluid pressures in the first and second pump chambers).

(9) The fluid pressures of the first and second pump chambers (Dout1, Dout2) are controlled at different pressure levels, and the partition (400) is held immovable in the axial direction and in the rotational direction. Therefore, this tandem pump can prevent volume changes in the first and second pump chambers, and thereby reduce the friction and the leak of the operating fluid.

Embodiment 2

The second embodiment is substantially identical, in the basic construction and arrangement in the hydraulic circuit, to the first embodiment shown in FIGS. 1˜7. The second embodiment is different from the first embodiment in that, instead of the fastening devices (bolts B) for fastening cover member 20 to main housing member 10, the cover member 20 according to the second embodiment is formed with a threaded portion (23) and screwed into a mating threaded portion (16) of main housing member 10.

FIG. 8 shows a tandem pump P according to the second embodiment in an axial section (in place of FIG. 4 of the first embodiment). Cover member 20 of FIG. 8 includes a threaded portion 23 formed externally in the outer circumference of the cylindrical projecting portion 21. On the other hand, main housing member 10 includes a threaded portion 16 formed internally in the inside cylindrical surface defining the larger portion 15 of the pump receiving portion 12. In this example, the externally threaded portion 23 includes a male screw thread while the internally threaded portion 16 includes a corresponding female screw thread.

Cover member 20 is fixed to main housing member by screwing the externally threaded portion 23 into the internally threaded portion 16 formed in the surrounding wall formed by main housing member 10. Cover member 20 abuts on center plate 400 axially with the forward end 22 of cylindrical projecting portion 21, and thereby determines the position of center plate 400 in the same manner as in the first embodiment, so that the same effects can be obtained.

Embodiment 3

The third embodiment is substantially identical, in the basic construction and arrangement in the hydraulic circuit, to the first embodiment. The third embodiment is different from the first embodiment in that the center plate 400 is divided into two plates (400P, 400S).

FIG. 9 is a sectional view similar to FIG. 4, but showing the tandem pump of the third embodiment. FIGS. 10 and 11 are perspective views showing, respectively, a first center plate 400 p on the z positive side, and a second center plate 400S located on the z negative side of first center plate 400P.

Although seal members 34 and 35 are provided in the outer circumferences of drive and driven shafts 110 and 120 in the first embodiment, the seal members 34 and 35 according to the second embodiment are fit, respectively, in (annular) seal grooves 401 a and 402 a formed in the inner circumferences of drive shaft through hole 401S and driven shaft through hole 402S of second center plate 400S.

Second center plate 400S includes a larger disc portion having an annular z positive surface (K), and a center projecting portion projecting in the z positive direction from a central region of the larger disc portion, and having an z positive end surface (K, N). First center plate 400P includes a smaller disc portion forming the smaller section 420, an outside flange 410′ forming the step 410, and a center recess which is recessed from the z negative side of first center plate 400P in the z positive direction and which is adapted to receive the center projecting portion of second center plate 400S fittingly. Therefore, the center plate 400 is divided into first and second center plates 400P and 400S in a parting plane K (shown by a solid line in FIG. 9) composed of an outer annular flat region in which a flat annular z negative surface of the flange 410′ of first center plate 400P abuts on a flat annular z positive surface of the larger disc portion of second center plate 400S, and a central flat region which extends in an imaginary flat plane N parallel to the x-y plane whereas the outer annular flat region of the parting plane K is located on the z negative side of the flat plane N. In the center flat region of the parting plane K, the flat z positive side surface of the center projecting portion of second center plate 400S abuts on or confronts the (flat) bottom of the center recess of first center plate 400P. The center flat region of parting plane K extends around the drive shaft 110 and driven shaft 120. Thus, parting plane K includes a step K1 between the outer annular region and the center region. The first and second grooves 401 a and 402 a are opened in the center region of parting plane K at 401 b and 402 b, respective, to the z positive side. The imaginary plane N is located on the z positive side of the step 13 of main housing member 10, and the center projecting portion of second center plate 400S extends beyond the axial position of step 31, to the z positive side. The outer annular flat region of parting plane K is located on the z negative side of the axial position of step 13 whereas the central flat region of parting plane K is located on the z positive side of the axial position of step 13 of main housing member 10.

The z positive side surface of flange 410′ of first center plate 400P abuts on the step 13 of main housing member 10, and thereby positions first center plate 400P securely. Therefore, even if first center plate 400P is pushed in the z positive direction because of leak from the S route discharge circuit 20 h located on the z negative side of step 410 (410′), the first center plate 400P is held immovable at the correct position without increasing the friction with the first driving and driven gears 130P and 140P.

The parting plane K includes regions forming z positive side 401 a of 402 b of seal grooves 401 a and 402 a. Thus, the seal grooves 401 a and 402 a are open in the parting plane K, toward the z positive side, and the seal members 34 and 35 are bared in the z positive side surface of second center plate 400S. Therefore, seal members 34 and 35 can be fit readily in the respective grooves at the time of the assembly.

The (annular) forward end 22 of cover member 20 abuts on the outer annular region 433 of the larger disc portion of second center plate 400S as in the first embodiment. The flange 410′ of first center plate 400P and the larger disc portion of second center plate 400S form the larger section of the center plate clamped between the step 13 of main housing member 10 and the cylindrical projecting portion 21 of cover member 20, as in the first embodiment. Thus, first and second center plates 400P and 400S are positioned and fixed immovable as a single unit in the z direction.

In the tandem pump according to the first embodiment, the S route discharge circuit 20 h is formed by drilling in center plate 400. In the illustrated example of the third embodiment, the S route discharge circuit 20 h is formed partly by one or more cutout portion 411 formed in the flange 410′ of first center plate 400P.

The cutout portion 411 is connected with an oil passage (424) of second center plate 400S. This oil passage (424) is opened by drilling like oil passage 20 h of the first embodiment, and connected with the suction region Din2 of second pump P2. Thus, this oil passage (424) and cutout portion 411 form the S route discharge circuit 20 h.

It is possible to form one or more cutout portion 411 in first center plate 400P readily (without the need for adding a special manufacturing step) by forming the shape of the cutout portion in a mold for forming first center plate 400P at the time of forming the mold (by sintering, for example).

In the example of FIGS. 9-11, the step 410 and smaller section 420 are formed in first center plate 400P, and the larger section 430 is formed in second center plate 400S. Like center plate 400 of the first embodiment, the smaller section 420 of first center plate 400P includes the z positive side which includes the sliding surface 421 a and the seal block abutting surface 421 b. The larger section 430 of second center plate 400S includes the z negative side 431 including the sliding surface 431 a and the seal block abutting surface 431 b.

In the example of FIGS. 9˜11 according to the third embodiment, the plate member (400) of the partition includes a first plate member (400P) formed with a through hole (401P) for receiving the rotation shaft (110), a second plate member (400S) formed with a through hole (401S) for receiving the rotation shaft, and a seal groove (401 a) which is formed (axially) between the first and second plate members and which receives a seal member (34) surrounding the rotation shaft (110). Therefore, the third embodiment can provide the same effects as the first embodiment. Furthermore, it becomes easier to form the center plate (400) with smaller molds for the first and second plate members (400P, 400S). The seal member (34) is bared in a parting plane (K) between the first and second plate members, so that it is easier to fit the seal member in the seal groove (401 a). Seal member 35 can be fit easily in the seal groove 402 a in the same manner.

Embodiment 4

According to a fourth embodiment, the center plate 400 and main housing member 10 are formed as a single integral member. As in the first, second and third embodiments, the main housing member 10 is made of softer metallic material (aluminum alloy) and the rotating elements of the pump (130, 140) are made of harder metallic material (Fe based material).

FIG. 12 shows the tandem pump P according to the fourth embodiment in the form of an axial section. The main housing member 10 shown in FIG. 12 includes a center partition wall serving as center plate 400. The center wall is formed with the drive shaft through hole 401 and the driven shaft through hole 402. The main housing member 10 includes a z positive (first) side surface formed with a first recessed portion 12 d recessed in the z negative direction from the z positive side surface facing in the z positive direction, and a z negative (second) side surface formed with a second recessed portion 12 c recessed in the z positive direction from the z negative side surface of the main housing member 10. The first side plate 150 is disposed in the first recessed portion 12 d, and the second side plate 160 is disposed in the second recessed portion 12 c.

The center plate 400 is integral with the main housing member 10, so that the partition formed by the center plate 400 is stationary relative to main housing member 10. Therefore, cover member 20 is not required to abut against the center plate 400 unlike the preceding embodiments. In the example of FIG. 12, the forward end 22 of the cylindrical projecting portion 21 of cover member 20 is spaced from center plate 400. Accordingly, it is not necessary to increase the rigidity of the forward end 22 of cover member 20, and it is possible to reduce the wall thickness of cover member 20.

Since center plate 400 is integral with main housing member 10, it is not possible to insert the pump assembly 100 from the z negative side into main housing member 10. Instead, the first and second side plates 150 and 160 are inserted, respectively, from the z positive side and the z negative side. Therefore, there is provided an additional cover member 30 on the z positive side, in addition to the cover member 20 on the z negative side. The additional cover member 30 covers the first recessed portion 12 d and thereby defines the first discharge region Dout1 liquid-tightly. Seal members 34 and 35 for sealing the first and second pumps P1 and P2 from each other are provided around drive shaft 110 and driven shaft 120 as in the first embodiment. In the fourth embodiment, main housing member 10 includes the surrounding wall and partition, the cover member 20 include the second end wall and the additional cover member 30 includes the first end wall. The projecting portion 21 of cover member 20 is inserted in the second recessed portion 12 c which is larger in sectional size or diameter than the first recessed portion 12 d in the example of FIG. 12.

A first slide member 440 is provided between the partition 400 and the first driving and driven gears 130P and 140P in the first recessed portion 12 d. A second slide member 440 is provided between the partition 400 and the second driving and driven gears 130S and 140S in the second recessed portion 12 c. Since it is troublesome to form sliding surfaces in the partition 400 of FIG. 12, the slide members 440 are used to reduce the friction and improve the sliding contact characteristic without the need for an accurate finishing operation for forming sliding surfaces in center plate 400.

According to the fourth embodiment, the partition (400) is integral with the housing (1). Therefore, the fourth embodiment can determine the position of the partition securely, and provide the same effects as in the first embodiment. Moreover, the use of the partition integral with the housing reduces the number of component parts. The fourth embodiment eliminates or reduce the need for increasing the rigidity of the cover member (20) which is not required to press the partition. In the fourth embodiment, it is possible to eliminate the seal members 31 and 32 to be provided around the center plate 400 (shown in FIG. 4). With the slide members (440), it is possible to reduce the friction without the need for forming a precisely finished sliding surface in the center plate.

Embodiment 5

In the illustrated examples of the preceding embodiments, the tandem pump P is a combination of external gear pumps. According to a fifth embodiment, by contrast, the tandem pump P is a combination of internal gear pumps.

FIG. 13 shows the tandem pump P according to the fifth embodiment in axial section. This tandem pump P includes a first internal gear pump P1 including first inner rotor 510P and a first outer rotor 520P, and a second internal gear pump P2 including a second inner rotor 510S and a second outer rotor 520S.

The first and second inner rotors 510P and 510S are connected with and driven by the single common drive shaft 110. First and second inner rotors 510P and 510S are engaged, respectively, with first and second outer rotors 520P and 520S, and arranged to produce the respective discharge fluid pressures independently. Unlike the examples of the external gear pumps, the tandem pump P of FIG. 13 does not include the driven gear (120).

The main housing member 10 of FIG. 13 includes the pump receiving portion 12 shaped like a hollow cylinder having a bottom as in the illustrated example of the first embodiment. The pump assembly 10 including first pump P1, center plate 400 and second pump P2 is inserted into this pump receiving portion from the z negative side, and the pump receiving portion 12 is closed by the cover member 20 as in the illustrated example of the first embodiment.

The center plate 400 is substantially cylindrical, and includes an externally threaded portion 15a in the outer circumference. On the other hand, the surrounding wall of main housing member 10 includes an internally threaded portion 12 e in the inside wall of pump receiving portion 12. Center plate 400 is positioned and fastened in main housing member 10 by screwing the externally threaded portion 15 a of center plate 400 into the internally threaded portion 12 e of main housing member 10. In this example, the step 410 is made smaller.

The surrounding wall of main housing member 10 includes a first wall portion surrounding and defining the first (smaller) portion 14 of pump receiving portion 12, and a second wall portion surrounding and defining the second (larger) portion 15(which is greater in the cross sectional size than the first portion 14). In the example of FIG. 13, the internally threaded portion 12 e formed in the second (larger) portion 15, so that main housing member 10 can position the center plate 400 securely.

In the example of FIG. 13, the surrounding wall of main housing member 10 includes a third wall portion surrounding and defining a third portion which is greater in the cross sectional size than the second portion 15. Correspondingly, the center plate 400 of FIG. 13 includes a first portion, a second portion which is greater in cross sectional size than the first portion and which is formed with the externally threaded portion 15 a, and a third portion which is greater in cross sectional size than the second portion. The second portion formed with the externally threaded portion 15 a is located axially between the first portion provided with a seal ring (31) and the third portion provided with a seal ring (32).

It is possible to employ the internal gear pumps in the first, second, third and fourth embodiments, instead of the external gear pumps. The fixing structure using the externally threaded portion 15 a and the internally threaded portion 12 e can be applied to the first through fourth embodiments.

This application is based on a prior Japanese Patent Application No. 2008-058970 filed on Mar. 10, 2008. The entire contents of this Japanese Patent Application are hereby incorporated by reference.

Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art in light of the above teachings. The scope of the invention is defined with reference to the following claims. 

1. An apparatus comprising a tandem pump which comprises: a rotation shaft extending in an axial direction; first and second pump sections driven by the rotation shaft; a housing defining a pump receiving portion including a first pump chamber receiving the first pump section and a second pump chamber receiving the second pump section; and a partition separating the first and second pump chambers from each other, the partition being positioned in the axial direction by the housing.
 2. The apparatus as claimed in claim 1, wherein the housing is arranged to regulate rotation of the partition.
 3. The apparatus as claimed in claim 2, wherein the housing includes a main housing member including the pump receiving portion and a cover member closing the pump receiving portion.
 4. The apparatus as claimed in claim 3, wherein the partition includes a plate member which is separate from the housing and which includes an outer circumferential portion clamped between the housing main member and the cover member so that the position of the partition is fixed by being clamped.
 5. The apparatus as claimed in claim 4, wherein the main housing member includes a surrounding wall surrounding the pump receiving portion including a first portion having a smaller sectional size, a second portion having a larger sectional size greater than the smaller sectional size, and a step which is formed between the first and second portions of the pump receiving portion and which is arranged to abut against the plate member of the partition so that the plate member is clamped between the step and the cover member.
 6. The apparatus as claimed in claim 3, wherein the housing includes an internally threaded portion formed inside the pump receiving portion, and the partition is a plate member which is separate from the housing, the plate member including an externally threaded portion which is formed on an outer circumference of the plate member and which is screwed in the internally threaded portion of the housing so that the position of the plate member is fixed.
 7. The apparatus as claimed in claim 6, wherein the main housing member includes a surrounding wall which surrounds the pump receiving portion including a first portion having a smaller sectional size, a second portion which has a larger sectional size greater than the smaller sectional size, and which includes the internally threaded portion formed in the second portion.
 8. The apparatus as claimed in claim 5, wherein the plate member of the partition includes a first plate member, a second plate member, and a seal groove which is formed between the first and second plate member and which receives a seal member surrounding the rotation shaft.
 9. The apparatus as claimed in claim 3, wherein the partition is formed as an integral part of the housing.
 10. The apparatus as claimed in claim 9, wherein the housing is made of an aluminum alloy, the first and second pump sections are made of a ferrous material, and a slide member is provided between the partition and each of the first and second pump sections.
 11. The apparatus as claimed in claim 5, wherein each of the first and second pump sections includes a driving gear drivingly connected with the rotation shaft and a driven gear engaged with the driving gear, the first pump section is interposed between a first side plate and a first side portion of the partition, the second pump section is interposed between a second side plate and a second side portion of the partition, and the first and second side portions are integral parts of the partition.
 12. The apparatus as claimed in claim 3, wherein the apparatus is further comprises: a wheel cylinder set including a first subset including a first wheel cylinder provided for braking a first wheel of a vehicle and a second subset including a second wheel cylinder provided for braking a second wheel of the vehicle; and a hydraulic system including a first subsystem including a first control valve and connecting the first pump section with the first wheel cylinder to increase a fluid pressure of the first wheel cylinder, and a second subsystem including a second control valve and connecting the second pump section with the second wheel cylinder to increase a fluid pressure of the second wheel cylinder.
 13. The apparatus as claimed in claim 1, wherein the partition is arranged to separate the first and second pump chambers from each other in a liquid-tight manner to enable control of fluid pressures in the first and second pump chambers at different pressure levels, and the housing is arranged to fix the position of the partition in the axial direction and in a radial direction of the rotation axis.
 14. An apparatus comprising a tandem pump which comprises: a rotation shaft extending in an axial direction; first and second pump sections driven by the rotation shaft; a housing defining a pump receiving portion including a first pump chamber receiving the first pump section and a second pump chamber receiving the second pump section; a partition located axially between the first and second pump chambers, and volume change preventing means for preventing volume change of the first and second pump chambers by preventing the partition from being moved in the axial direction relative to the housing. 